This invention relates to self-propelled institutional or commercial type lawn mowers, and is especially directed to large lawn mowers intended for extended service on a daily basis, e.g., by commercial landscape gardeners or ground maintenance personnel responsible for attending to lawns at corporate or government office parks, golf courses, condominiums, and the like. The invention is especially directed to walk-behind and sulky-type riding mowers in which there is an operator position situated behind the mowing mechanism.
At present, lawn mowers of this type employ belt drives both for the mower blade and for the drive wheels. In these current mowers, each wheel is belt driven and is provided with a clutch and an individual wheel-brake which are intimately linked. The belts wear out quickly and the drive thus has a high maintenance rate. The belts also tend to slip when the grass is wet. Changing speeds requires disengaging both belts by squeezing hand calipers found on each handle bar. A speed selector control must then be adjusted to effect speed change. Because these actions take considerable time to accomplish, the operator generally opts not to make speed changes. This, however, renders precision mowing near obstacles difficult or impossible. Consequently, an intolerable amount of follow-up mowing with a hand mower or trimmer is usually required. The operator must also release his grip on the steering controls when making various machine adjustments; this can and often does lead to an accident.
These same hand calibers when squeezed to their maximum positions engage a brake which is used for turning purposes. Because the hand calipers are spring-controlled, they require considerable hand pressure to engage. This continuous hand pressure is extremely tiring. Almost continuous squeezing is required to keep the mower steering in the proper direction due to the direct-drive, non-differential type axle.
Previous walk-behind mowers generally do not have a reverse speed. Because of the excessive weight of these mowers and their uneven weight distribution, manual backing of the mower is extremely tiring on the operator and is often dangerous.
An improved mower that employs a hydrostatic transmission has been proposed in U.S. Pat. No. 4,787,195. That patent describes a self-propelled lawn mower that has a mowing deck that supports one or more mowing blades. A pair of drive wheels are rotatably supported in a power deck located behind the mowing deck. Drive linkages convey power from an engine mounted upon the power deck to the rear drive wheels and also to a blade drive system for rotating the mowing blades. An operator position is situated rearward of the drive wheels. The mower includes a handle arrangement behind the drive wheels with operator controls mounted on the handle for selectively controlling the speed and direction of the drive wheels. In the mower of that patent, a hydrostatic transmission has an input shaft driven by the engine, an output shaft arranged to turn the drive wheels, and a control shaft that is rotated to control the ratio of the output shaft speed to the input shaft speed in a continuous range of speed from reverse, through neutral, to maximum forward speed. The operator controls include a transmission control lever that is connected, for example, via a cable or a rigid linkage, to the control shaft of the hydrostatic transmission to enable the operator to select a desired drive wheel speed without removing his or her hand from the steering handle. The input shaft of the hydrostatic transmission can be vertically disposed, and the control shaft is either vertically or transversely disposed. A control lever for the hydrostatic transmission can be a C-shaped or L-shaped member that is connected at one end to the control shaft, with a control cable being connected between the control handle and this member. A cooling fan can be mounted on the shaft of the hydrostatic transmission for air cooling the same. The drive wheels are connected to the hydrostatic transmission through a differential-type drive system whose differential right and left output shafts serve as axles on which the drive wheels are mounted. These output shafts are provided with independent right and left disc brakes, with separately actuated operating levers, so that the operator can brake the wheels independently for precision steering of the mower.
The engine is mounted with its center of gravity rearward of the drive wheel shaft, to serve as a counterweight or counterpoise to balance the weight of the mowing deck. Consequently, the mower center of gravity is disposed at or close to the drive wheel axle. This aids traction significantly and facilitates steering of the machine.
The hydrstatic-drive mower can be steered in either two ways:
1. Because of the differential drive, the operator can simply apply body weight to the handle bars to make directional changes. This is impossible with previous mowers because their wheels are not differentially coupled to the drive shaft.
2. Each wheel is fitted with a disc brake which is engaged by means of a hand lever on a corresponding handle grip. Engaging the disc brake is much easier than engaging the hand brake on other mowers because there is no spring-actuated clutch in the disc brake linkage. Squeezing a selected hand caliper to engage one of the disc brakes results in an almost effortless turn toward the braked-wheel side of the machine.
These mowers can quickly turn one-hundred-eighty degrees to mow a row alongside a just-mowed row. To do this, the operator simply squeezes one brake lever, and releases the grip of the other hand. The differential drive than pulls the mower around and, and when turned, the operator simply releases the brake lever and resumes mowing.
Unfortunately, the effect of the differential drive is to transfer all of the power to the unbraked wheel at double the wheel speed that was experienced when both wheels were unbraked. This makes the mower rather difficult to control, unless the transmission control can be moved to a lower setting to keep the wheel speed even. However, in the arrangement of U.S. Pat. No. 4,787,195, the control lever is on one side of the handle bar, the operator can effect a hand brake turn only in one direction, i.e. only to the right where the control lever is mounted near the right hand grip.